Characterization of Zhundong subbituminous coal by time-of-flight mass spectrometry equipped with atmospheric pressure photoionization ion source

Zhundong subbituminous coal pretreated with aqueous H2O2 was oxidized by aqueous NaOCl and sequentially extracted with diethyl ether (DEE) and ethyl acetate (EA) to afford DEE- and EA-extractable fractions and residue. Both extracts were esterified with CH2N2 and analyzed using high performance liquid Chromatography/mass spectrometry equipped with electrospray ionization (ESI) or atmospheric pressure photoionization (APPI) ion source. Molecular mass of 60% compounds in the esterified extracts ranged between 200 and 600 Da and more than 20% of the esterified extracts had molecular mass over 600 Da. Toluene and toluene/anisole (vol./vol. = 95/5) were used as dopants for APPI. Low- and non-polar compounds in the esterified extracts were well analyzed using APPI/MS. Compared to toluene/anisole mixture, toluene greatly increased ionization efficiency of APPI. More molecular associations were detected by ESI than by APPI. Heteroatoms were identified in most of the associated species.